Pentostatin (2'-Deoxycoformycin) is a tight-binding inhibitor of adenosine deaminase which has been used as a therapeutic agent for a number of disorders including hairy cell leukemia. Our hypothesis is that Pentostatin will be an effective agent for the treatment of refractory rheumatoid arthritis at doses that have little or no toxicity through inhibition of the proliferation of T-lymphocytes.